Windows: official port -- UCRT static build, UTF-8 throughout, Low IL sandbox, ncurses TUI, installer; v0.6.0

Build
  * cross build switches to pkgsCross.ucrt64 (shell-win.nix); curl (Schannel),
    winpthreads and ncurses 6.6 are linked statically, so the release is
    cst-agent.exe + busybox.exe (busybox-w32 Unicode) with no extra DLLs
  * windres embeds a manifest with activeCodePage=UTF-8 and a version resource
  * ncurses 6.6 Windows console driver patches (mouse button state, A_DIM,
    wide-char declarations): scripts/patches/
  * scripts/bootstrap_msys2.sh builds the same release natively in MSYS2
    UCRT64; PR #1's MINGW64 notes now point there
  * vendor/tre-regex (musl's TRE) provides <regex.h> on MinGW

UTF-8
  * paths cross the system call boundary as UTF-16 (*W APIs); console code
    pages set to 65001 and restored on exit; files are read and written in
    binary mode
  * child output that is not valid UTF-8 is decoded from the console, OEM or
    ANSI system code page
  * read_file hides CR; edit_file, apply_patch and write_file keep CRLF line
    endings and a UTF-8 BOM

OS layer and processes
  * os_dir_* and cst_fnmatch replace the POSIX-only directory walks in
    subagent, plugins, skills, undo and fs_tools; realpath / path_under and
    symlink rejection work on Windows
  * every child goes through CreateProcessW with its own environment block
    inside a Job Object, so timeouts and Esc end the whole process tree

Sandbox (auto mode, "auto · lowil")
  * run_shell runs with a restricted Low integrity token; the workspace gets
    an inheritable Low label once, the sandbox TEMP is labeled Low, and the
    credentials file gets a no-read-up label
  * drive roots, the profile and system folders are never labeled
  * network commands still ask, since Low IL does not block the network;
    Access denied and MSYS2's 0xc0000142 offer a rerun outside the sandbox
  * /sandbox lists labeled folders, /sandbox reset-labels restores them

TUI
  * raster console fonts are switched to Consolas / NSimSun while running
  * the home logo falls back to text when the console font lacks U+2580
  * mouse drag copy goes to the Windows clipboard

Distribution
  * scripts/install_windows.ps1 installs a Gitea release into
    %LOCALAPPDATA%\Programs\cst-agent and adds it to the user PATH;
    cst-agent-update.cmd reruns it; scripts/release_windows.sh uploads the
    zip with the token taken from the environment
  * scripts/run_windows.bat is gone; docs/README-windows.md is rewritten

Tests
  * new test_lowil, test_win_utf8 and test_os_dir; tests made portable
    (cst_test_util.h)
  * scripts/win_test.sh and scripts/winvm/ run the suite on English and
    Chinese Windows Server VMs as Administrator, a standard user and a
    Chinese user name: 29/29 on all six

src/agent_store.c

@@ -6,7 +6,6 @@
 #include "cst_agent.h"
 #include "os_compat.h"
 
-#include <dirent.h>
 #include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -45,7 +44,7 @@ int cst_agent_store_ensure(const char *workspace) {
   char gi[OS_PATH_MAX];
   if (os_path_join(gi, sizeof(gi), base, ".gitignore") == 0 &&
       OS_ACCESS(gi, OS_F_OK) != 0) {
-    FILE *fp = fopen(gi, "w");
+    FILE *fp = fopen(gi, "wb");
     if (fp) {
       fputs("*\n", fp);
       fclose(fp);
@@ -97,7 +96,7 @@ int cst_agent_store_set_current(const char *workspace, const char *id) {
     return -1;
   if (os_path_join(path, sizeof(path), dir, "CURRENT") != 0)
     return -1;
-  FILE *fp = fopen(path, "w");
+  FILE *fp = fopen(path, "wb");
   if (!fp)
     return -1;
   fprintf(fp, "%s\n", id);
@@ -113,7 +112,7 @@ int cst_agent_store_get_current(const char *workspace, char *id_out,
     return -1;
   if (os_path_join(path, sizeof(path), dir, "CURRENT") != 0)
     return -1;
-  FILE *fp = fopen(path, "r");
+  FILE *fp = fopen(path, "rb");
   if (!fp)
     return -1;
   if (!fgets(id_out, (int)id_sz, fp)) {
@@ -159,7 +158,7 @@ int cst_agent_store_list(const char *workspace, char ids[][128], int max_ids) {
   char dir[OS_PATH_MAX];
   if (cst_agent_store_dir(workspace, dir, sizeof(dir)) != 0)
     return 0;
-  DIR *d = opendir(dir);
+  os_dir_t *d = os_dir_open(dir);
   if (!d)
     return 0;
   typedef struct {
@@ -168,23 +167,23 @@ int cst_agent_store_list(const char *workspace, char ids[][128], int max_ids) {
   } ent_t;
   ent_t *ents = calloc((size_t)max_ids * 4, sizeof(ent_t));
   int n = 0, cap = max_ids * 4;
-  struct dirent *de;
-  while ((de = readdir(d)) != NULL) {
-    size_t len = strlen(de->d_name);
-    if (len < 7 || strcmp(de->d_name + len - 6, ".jsonl") != 0)
+  const os_dirent_t *de;
+  while ((de = os_dir_next(d)) != NULL) {
+    size_t len = strlen(de->name);
+    if (len < 7 || strcmp(de->name + len - 6, ".jsonl") != 0)
       continue;
     if (n >= cap)
       break;
     snprintf(ents[n].id, sizeof(ents[n].id), "%.*s", (int)(len - 6),
-             de->d_name);
+             de->name);
     char full[OS_PATH_MAX];
-    if (os_path_join(full, sizeof(full), dir, de->d_name) != 0)
+    if (os_path_join(full, sizeof(full), dir, de->name) != 0)
       continue;
     struct stat st;
     ents[n].mtime = (stat(full, &st) == 0) ? st.st_mtime : 0;
     n++;
   }
-  closedir(d);
+  os_dir_close(d);
   for (int i = 0; i < n; i++) {
     for (int j = i + 1; j < n; j++) {
       if (ents[j].mtime > ents[i].mtime) {
@@ -218,7 +217,7 @@ int cst_agent_store_title_set(const char *workspace, const char *id,
     return -1;
   if (!title || !title[0])
     return remove(p) == 0 || errno == ENOENT ? 0 : -1;
-  FILE *fp = fopen(p, "w");
+  FILE *fp = fopen(p, "wb");
   if (!fp)
     return -1;
   for (const char *c = title; *c; c++)
@@ -255,7 +254,7 @@ int cst_agent_store_info(const char *workspace, const char *id,
   info->mtime = (long long)st.st_mtime;
   char tp[OS_PATH_MAX];
   if (side_path(workspace, id, ".title", tp, sizeof(tp)) == 0) {
-    FILE *tf = fopen(tp, "r");
+    FILE *tf = fopen(tp, "rb");
     if (tf) {
       if (fgets(info->title, sizeof(info->title), tf)) {
         size_t n = strlen(info->title);
@@ -265,7 +264,7 @@ int cst_agent_store_info(const char *workspace, const char *id,
       fclose(tf);
     }
   }
-  FILE *fp = fopen(p, "r");
+  FILE *fp = fopen(p, "rb");
   if (!fp)
     return 0;
   size_t cap = 1 << 16;
@@ -311,16 +310,16 @@ int cst_agent_store_delete(const char *workspace, const char *id) {
     remove(p);
   /* sub-agent transcripts live in <id>/ */
   if (side_path(workspace, id, "", p, sizeof(p)) == 0) {
-    DIR *d = opendir(p);
+    os_dir_t *d = os_dir_open(p);
     if (d) {
-      struct dirent *de;
-      while ((de = readdir(d)) != NULL) {
+      const os_dirent_t *de;
+      while ((de = os_dir_next(d)) != NULL) {
         char f[OS_PATH_MAX];
-        if (strncmp(de->d_name, "sub-", 4) == 0 &&
-            os_path_join(f, sizeof(f), p, de->d_name) == 0)
+        if (strncmp(de->name, "sub-", 4) == 0 &&
+            os_path_join(f, sizeof(f), p, de->name) == 0)
           remove(f);
       }
-      closedir(d);
+      os_dir_close(d);
       rmdir(p);
     }
   }